1. Field of the Invention
This invention relates to a resistance device for a bicycle exerciser, more particularly to a wheel-type resistance device which provides a magnetic resisting force between a flywheel and a dragging force adjusting member thereof.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a conventional wheel-type resistance device of a bicycle exerciser includes a flywheel 2 which rotates together with a hub member 9 around an axle 1. The flywheel 2 has an accommodation chamber 2a which is indented axially to form an inner peripheral wall 2b around the axle 1. Two magnetically permeable members 6 are secured on the inner peripheral wall 2b. A dragging force adjusting member 3 is sleeved slidably on the axle 1 and has an outer peripheral wall 3b provided with a plurality of arcuate magnets 7 opposite to the magnetically permeable members 6. When the hub member 9 is rotated by a pedaling action of a user to rotate the flywheel 2, the magnets 7 are drawn by the magnetically permeable members 6 to generate a magnetic dragging force.
A guiding seat 5 is secured to the exerciser and has a rail arm 5b which passes through a through hole 3a in the adjusting member 3. A cable 8 has one end 8a connected to the adjusting member 3, and an opposite end mounted on the bicycle exerciser and operable so as to pull the adjusting member 3 away from the flywheel 2 in the axial direction by the guidance of a guiding rail 5b to decrease the opposing surfaces of the magnetically permeable members 6 and the magnets 7 decrease in turn the magnetic dragging force (as shown in the dotted lines of FIG. 1). A coil spring 4 is sleeved on the axle 1 to bias the adjusting member 3 toward the flywheel 2 against the action of the cable 8.
The drawbacks of the conventional resistance device are as follows:
1. The biasing force of the coil spring 4 must be overcome when moving the adjusting member 3, thereby resulting in inconvenience during operation. PA1 2. The size of the clearance between the inner and outer peripheral wall 2b, 3b must be very precise. A relatively large clearance will affect adversely the magnetic dragging force, and is liable to contamination. PA1 3. The movement of the adjusting member 3 is guided only by the rail arm 5b and tends to be oblique relative to the axle 1, thereby resulting in possible contact between the magnets 7 and the magnetically permeable members 6, and in the generation of noise. PA1 4. Each of the magnetically permeable members 6 is bent to be semi-circular in shape, thereby resulting in increased difficulties during manufacture and assembly.